The present invention relates to thermoformable, multilayer acrylonitrile-butadiene-styrene (ABS) resin sheets, equipment liners, and insulative equipment systems. More particularly, the present invention relates to thermoformable, multilayer ABS sheets and thermoformed equipment liners obtained therefrom which are used with foamed-in-place insulation in insulative equipment systems.
Acrylonitrile-butadiene-styrene resins comprise three building blocks, acrylonitrile, butadiene, and styrene which allow for variation in properties such as chemical resistance, heat stability, impact resistance, and toughness, rigidity, and processing ease, depending on the percentages of the three major components therein and the additives used. In addition to providing useful properties to the finished products, ABS resins can be easily processed to finished parts such as by coextrusion, sheet extrusion, thermoforming, blow molding, profile extrusion, and injection molding. Because of its versatility, ABS is used in a wide variety of applications, such as equipment liners, in that it provides strong, durable shielding in many environments. Typical equipment liners include automotive interior trim, business machine housings, refrigerator liners, freezer liners, dishwasher liners, cooling chest liners and appliance housing liners. ABS resin is often the material of choice for its balance of strength, toughness (impact resistance), appearance (gloss and color), chemical resistance, processability, and price. For example, this balance of properties makes ABS extruded sheets the material of choice for thermoformed equipment liners such as the interior food compartments and door liners of refrigerators. Other major end uses of ABS thermoformed extruded sheet include dishwasher liners and interior and exterior parts for trucks, autos, boats, and mobile homes.
ABS provides deep draw capability for thermoforming operations, strength and toughness for durability in assembly and use, high gloss, stain and chemical resistance to items such as food. Sheet extrusion grades of-ABS are produced as low, medium, or high impact resins with various gloss levels ranging from high gloss to matte (low gloss). In many end uses, such as refrigerator liners, the ABS is exposed to foamed-in-place insulation during assembly. Foamed-in-place insulation typically generates a rush of blowing agent so as to foam the insulative material (polyurethane). This rush of blowing agent comes in contact with and permeates into conventional ABS liners, causing embrittlement and surface cracks. It is believed that the blowing agents utilized for the foamed-in-place insulation, particularly fluorohydrocarbons, more particularly hydrochlorofluorocarbons, degrade the ABS liner when they come in contact with the liner, causing it to crack, despite the chemical resistance and impact resistance of ABS resin. Methods for improving the resistance of ABS resin to these blowing agents, such as the utilization of a high level of acrylonitrile, often result in the loss of some advantages of ABS resin. Use of multilayered liners employing an ABS substrate layer and a layer of barrier material located between the ABS layer and the polyurethane foam can effectively protect the ABS layer, but can also result in difficulties when recycling the liners (and trim therefrom) as a blend material due to incompatibility between the barrier layer material and the ABS substrate layer material thereby making the liner economically and environmentally unattractive.
Accordingly, it is desirable to provide a multilayer equipment liner based on ABS resin which is more resistant to physical property degradation caused by foamed-in-place insulation as evidenced by maintenance of the ductile break impact properties of the liners and which is easily recycled by regrinding to yield a compatible blend composition.
It is therefore, an object of the present invention to provide thermoformable sheets based on acrylonitrile-butadiene-styrene resin which are resistant to degradation from the blowing agents used in foam-in-place insulation as evidenced by maintenance of impact strength and ductile break properties.
It is an additional object of the present invention to provide an equipment liner resistant to property loss from exposure to halogenated hydrocarbons blowing agents used for foamed-in-place insulation and which can be easily reground into a compatible blend material which may serve as a useful molding material.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
These and other objects are achieved by a thermoformable multilayer sheet which comprises an outer layer of a first ABS resin, and a protective inner layer of second ABS resin. Thermoformed equipment liners obtained from this multilayer sheet are also provided, and insulative equipment systems are also provided involving the liners and the insulative foam.